1. Field of the Invention
The present invention relates to an optical pickup device and a recording/reproducing device for at least either recording or reproducing information on/from an optical recording medium using near-field light.
2. Description of the Related Art
In recent years, much attention has been focused on a recording/reproducing method using near-field light in order to record/reproduce information on/from an information recording medium such as an optical disk, a magnetic disk, an optical memory card or the like at high density and high resolution. Near-field light is a kind of light leaked from an object on a light-irradiating side when the distance between the object on the light-irradiating side and an object on a light-irradiated side is smaller than a specified value. Near-field light is also called “evanescent wave”.
Various proposals have been made as methods of recording/reproducing information by irradiating near-field light onto the information recording medium. Such proposals include, for example, methods of recording/reproducing information using a SIL (Solid Immersion Lens), a SIM (Solid Immersion Mirror), a waveguide structure or the like (see, for example, Patent Document: Japanese Unexamined Patent Application Publication No. 5-189796 and Non-Patent Document: “Near-Field Phase-Change Optical Recording of 1.36 Numerical Aperture”, I. Ichimura et al., Japanese Journal of Applied Physics, Vol. 39, pp. 962-967, 2000). In the method of recording/reproducing information on/from an information recording medium capable of being recorded/reproduced at high density using a near-field light irradiating unit configured by a SIL and the like having a numerical aperture NA of more than 1, information is recorded/reproduced in a state where the distance between the lens and the surface of the information recording medium is reduced to a value small enough to cause the evanescent wave.
Various recording media such as a phase-change recording media, a read-only optical recording medium and the like are proposed to be used as the information recording medium for being recorded/reproduced at high density using near-field light (see, for example, Non-Patent Document: “High Density Near-Field Optical Disc Recording”, M. Shinoda et al., Digest of ISOM2004, We-E-03, and Non-Patent Document: “Progress in Electron Beam Mastering of 100 Gb/inch2 Density Disc”, M. Furuki et al., Japanese Journal of Applied Physics Vol. 43, pp. 5044-5046, 2004). The phase-change recording media has a configuration in which a reflective film formed of aluminum or the like, a dielectric layer formed of SiO2 or the like, a phase-change material layer formed of GeSbTe or the like and a dielectric layer formed of SiO2 or the like are sequentially laminated in this order on a substrate formed of glass, polycarbonate (PC) or the like. Further, the read-only optical recording medium has a configuration in which a reflective film formed of aluminum or the like is laminated on a substrate formed of glass, PC or the like, the substrate having rugged pits formed therein which correspond to recorded information. Further, in addition to the aforesaid optical recording media, other recording media such as a magneto-optical recording medium, an optical assistant magnetic recording medium and the like are also proposed to be used as the information recording medium for being recorded/reproduced using near-field light.
Further, it has been reported that, when using a near-field light irradiating unit configured by a SIL and the like, the distance between a lens-end-surface on the light-irradiating side and the surface of the optical recording medium is preferably no more than 1/10 of the wavelength of irradiation light (see, for example, Non-Patent Document: “A Simulation of Magneto-Optical Signals in Near-Field Recording”, K. Saito et al., Japanese Journal of Applied Physics, Vol. 38, pp. 6743-6749, 1999). For this reason, various researches have been conducted to develop a technology for precisely controlling a gap between the information recording medium and the SIL and the like, and develop a technology for performing a skew control to suppress collision of the SIL 141 and the like with the information recording medium while the information recording medium and the SIL 141 are moved relative to each other (see, for example, Japanese Unexamined Patent Application Publication No. 2001-76358 and Japanese Unexamined Patent Application Publication No. 2006-344351).
Further, in addition to the aforesaid recording/reproducing device of an information recording medium, an exposure device and the like using a SIL and the like have been proposed in the past (see, for example, Japanese Unexamined Patent Application Publication No. 2003-257052). The technology for precisely controlling the gap is also disclosed in Japanese Unexamined Patent Application Publication No. 2003-257052. According to this document, in the optical system of the exposure device, the focus position of a laser beam for detecting the gap is adjusted so that the laser beam is focused on an end surface of the SIL.